Rub the chicken breast with 0.5 tbsp olive oil, sea salt, black pepper, and garlic powder until evenly coated.
Preheat a grill or grill pan to medium-high heat and cook the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
While the chicken is grilling, dice the cucumber into bite-sized pieces, halve the cherry tomatoes, and finely mince the red onion.
In a small bowl, whisk together the remaining 0.5 tbsp olive oil and the lemon juice to create a simple, bright dressing.
Gently fold the cucumber, tomatoes, and red onion together in a medium bowl with the dressing and chopped fresh parsley.
Slice the avocado and add it to the salad just before serving to maintain its buttery texture and vibrant color.
Slice the grilled chicken into strips and serve immediately alongside the fresh cucumber and avocado salad.